The present invention relates to magnetic flowmeters. More specifically, the present invention relates to signal processing in a magnetic flowmeter.
Magnetic flowmeters measure the volumetric flow rate of a conductive fluid by determining the velocity of the fluid passing through a magnetic field. Magnetic flowmeter systems typically include a flow tube assembly and a transmitter assembly. The flow tube assembly is installed in a process piping line and includes a pair of conductance coils and a pair of electrodes. The coils are located on opposite sides of the cross section of the pipe and are energized by drive current from the transmitter. The drive current cause a magnetic field to be developed along a cross section of the pipe. The two electrodes are located across the pipe from each other along a line which is perpendicular the magnetic field. Fluid passing through the pipe is electrically conductive and the movement of the fluid through the magnetic field results in electrical potential or electromotive force (EMF) to be induced in the fluid which can be detected by the electrodes. This is in accordance with Faraday""s law of electromagnetic induction and the magnitude of the electric potential is proportional to the velocity of fluid.
The magnitude of the electric potential between the two electrodes is relatively small, particularly when measuring fluid having low conductivity. Noise in the electric potential can lead to inaccuracies in flow measurements. Various types of noise which can be present in the measurement signal include spikes, 1/f noise and white noise. Prior art techniques to eliminate noise includes the use of filters to provide a long damping time. However, although this improves measurement accuracy, it reduces the response time of the flowmeter. A method of improving the accuracy of magnetic flowmeters would be a significant improvement in the art, particularly if the method did not significantly lengthen the response time of the flowmeter.
A magnetic flowmeter includes a wavelet transformer for measuring flow which provides accurate flow measurement and a short response time. The flowmeter includes a flow tube assembly adapted to receive a fluid flow, a coil configured to apply a magnetic field to the fluid in the flow tube, and an EMF sensor having an EMF output related to an EMF generated in the fluid flow due to the applied magnetic field, velocity of the fluid and signal noise. A signal processor includes the wavelet transformer and is disposed to perform a wavelet transformation on the EMF output and provide a decomposition signal related to velocity of the fluid.